Police and protesters outside the Preston New Road drill site where Cuadrilla has been forced to temporarily stop fracking.
Photograph: Christopher Furlong/Getty Images

Cuadrilla has been forced to stop fracking after its operations at a well near Blackpool triggered an earthquake that breached the official threshold.

The company said it had paused work for 18 hours after the tremor on Friday morning. It was the 17th quake in the area since fracking began 11 days ago, but the first to be powerful enough to pass a regulatory threshold that requires fracking to stop.

Q&A

What is fracking?

Fracking, or hydraulic fracturing, is a way of extracting natural gas from shale rock formations that are often deep underground. It involves pumping water, chemicals and usually sand underground at high pressure to fracture shale – hence the name – and release the gas trapped within to be collected back at the surface.

The technology has transformed the US energy landscape in the last decade, owing to the combination of high-volume fracking – 1.5m gallons of water per well, on average – and the relatively modern ability to drill horizontally into shale after a vertical well has been drilled.

A red event is anything above 0.5 magnitude and requires Cuadrilla to stop injecting water and monitor the well for further seismic activity.

Any delays will cost the company financially. It has admitted that delays due to a legal challenge earlier this month were costing it £94,000 a day as workers stood idle.

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Cuadrilla said it was hydraulically fracturing shale rock adjacent to one of its horizontal wells when the tremor occurred. The integrity of the well was intact and regulators had been informed, it added.

The company intends to restart fracking on Saturday morning, though it only has permission to frack until 1pm on Saturdays.

In a statement, the firm said: “Micro-seismic events such as these result in tiny movements that are way below anything that would be felt at surface, much less cause any harm or damage.”

In total, there have been 17 tremors, two of which happened while fracking was under way and 15 of which happened afterwards and are known as “trailing” events.

Seismologists have been quick to note that all the tremors so far have been very small, with a 0.4-magnitude one on Monday akin to the vibrations from road traffic. Today’s 0.8-magnitude event was around 200 times smaller than a 2.3-magnitude one caused by fracking in 2011.

However experts have said the key thing is not whether people notice the quakes but whether they damage Cuadrilla’s well.

Stuart Haszeldine, professor of geology at the University of Edinburgh, said: “The practical significance is not whether these tremors are felt at the surface or not, but in the potential to damage the borehole, and the potential to create gas pathways from the shale towards larger faults, towards shallower aquifers, and to the surface.”

The Guardian revealed earlier this month that energy minister, Claire Perry, had proposed raising the regulatory threshold for tremors caused by fracking, as the industry begins to mature.

But the government has subsequently denied it has any plans to relax the rules. Lord Henley, a junior minister at the Department for Business, Energy and Industrial Strategy, said this week: “There are no plans to make changes to the traffic light system for monitoring induced seismicity.”